Described below are a method and an apparatus for the contactless determination of an electrical potential of an object.
It is known to measure the current flow through an object in a contactless manner. This can take place by way of inductive coupling, the Hall effect or the GMR (Giant Magneto Resistance) effect. In order to be able to measure contactless electrical output, aside from the contactless current measurement, a method for the contactless potential measurement is also required. The contactless potential measurement, in particular of high voltages, is inter alia particularly important in the field of smart metering, smart grid and response demand strategies.
So-called electric field meters provide one possibility. These use the effect of influence in order to be able to conclude the voltage to be determined by way of the determined electrical field strength. The distance between the object, the potential of which is to be determined, and the measuring electrode of the electric field meter and the material (dielectric layer) between the measuring electrode and object must however be made known precisely in the measuring capacitance. In order also to be able to measure direct voltages using an electric field meter, a shutter (field diaphragm) in the form of a chopper (impeller) is generally used between the measuring electrode and the object.
Capacitive voltage dividers can also be used to determine pure alternating voltages, wherein the coupling capacitance between a reference electrode and the potential to be measured must likewise be made known here.
Both methods and/or apparatuses (electric field meters and capacitive voltage dividers) presuppose precise knowledge of the coupling to the voltage to be measured, in particular the distance between measuring electrode and measuring object. In this respect, these known methods are unsuited to only temporary measuring processes or subsequent measuring installations. Electric field meters and capacitive voltage dividers are permanently installed for precise measurements and are calibrated in the installation surroundings. With manual measuring devices, precise knowledge of the geometry and material properties (line insulation, air, gas, condensation, etc.) of the measuring structure is required. To this end, special spacers are used with known electric field meters for instance. Spacers are nevertheless disadvantageous in that they do not rest directly on the conductive material, particularly for the potential determination of electrical insulated lines, and thus adjust the distance only to an inadequately precise degree. In addition, the type of insulating material cannot be taken into account. If this precision of the known contactless potential measuring methods is insufficient, it must be measured conventionally using contact.